In worldwide efforts to preserve a global environment, for example, regulations with respect to exhaust gas and fuel consumption in an internal combustion engine such as an engine of an automobile are further enhanced. Since a turbocharger feeds compressed air to an engine, in the turbocharger, it is possible to further decrease a volume displacement compared to natural intake. Accordingly, the turbocharger is a device which is remarkably effective to improve the fuel consumption and to decrease CO2.
In the turbocharger, since a turbine is rotated by exhaust gas of an engine, a delivery fan of a centrifugal compressor coaxially positioned with the turbine is rotated. Air which is compressed by the rotation of the delivery fan is decelerated by a diffuser, the pressure of the air is increased, and the air is supplied to an engine via a scroll flow path. A method for driving the turbocharger is not limited to the aspect in which the turbocharger is driven by exhaust gas. For example, various aspects such as an aspect in which the turbocharger is driven by an electric motor or an aspect in which the turbocharger is driven by a motor via a transmission are known.
The turbocharger includes a rotating shaft which connects a drive portion and the delivery fan of the centrifugal compressor to each other, and for example, a sliding bearing is used as a bearing of the rotating shaft and is used to be lubricated by a fluid. A bearing is configured of a radial bearing (journal bearing) which receives a radial load and a thrust bearing which receives a thrust load.
In the turbocharger, since regulation with respect to flue gas and a high-speed rotation for achieving a high output are required, a load to the rotating shaft is likely to increase. In addition, in the turbocharger which is driven by the exhaust gas, if an exhaust press increases, the load to rotating shaft is likely to increase. According to the increase of the load with respect to the rotating shaft, a friction loss when the rotating shaft rotates increases, a bearing loss increases, and there is a problem that performance of the turbocharger decreases.
Here, PTL 1 discloses a structure which has a so-called a floating disk which freely floats between a non-rotation type bearing housing which accommodates a shaft inside the bearing housing and a bearing comb which integrally rotates with the rotating shaft in a fluid type thrust bearing (axial bearing) of a rotatable rotating shaft. A relative speed difference in a fluid generated between the bearing housing and the bearing comb is decreased by the floating disk, shearing stress decreases, a friction resistance decreases, and a friction loss decreases.